Generally, in order to carry out a diagnosis of sleep apnea syndrome, for example, the user's state during sleep (hereinafter referred to as a sleep state) is estimated by using a body position sensor or a snore sensor, etc.
In this case, the body position sensor is attached to, for example, the user's chest, and the snore sensor is attached to, for example, the user's throat. Sleeping with a plurality of sensors separately attached at different parts of the body is very troublesome for the user.
Hence, recently, a sleep sensor (device) including a plurality of sensors to be used for estimating the user's sleep state has been developed. According to such a sleep sensor, not only the user's body position and respiratory state during sleep, but also other conditions such electrocardiographic activity, pulse waves, and body temperature can be estimated. Also, since it becomes unnecessary to attach a plurality of sensors separately as mentioned above, the burden on the user can be reduced.
Incidentally, the above-mentioned sleep sensor is often driven, by power supplied from a battery. In this situation, the sleep sensor must be driven by power supplied from the battery alone for a long time in order to estimate the user's sleep state as described above.
However, since the power supplied from the battery is limited, a mechanism for achieving power-saving in order to realize long-time driving of the sleep sensor including a plurality of sensors is desired.